Combustion apparatus and method



. J. BLOOMER COMBUSTION APPARATUS AND METHOD Filed Dec. 21

.uEy 10, 195i lill? INVENTR WWJZMf Patented July 10, `1951 COMBUSTIONAPPARATUS AND METHOD Ward J. Bloomer, Westfield, N. J., asslgnor to TheLummus ration of Delaware Company, New York,

N. Y., a corpo- Appllcation December 21,1950, Serial No. 202,015

s claims. (el. 11o-2s) This invention relates to combustion apparatusand methods of vortical fuel burning as generally set forth in mycopending applications for Patent Serial No. 66,445, filed December 21,1948, and Serial No. 98,976, filed June 14;' 1949. It is also acontinuation-in-part of my earlier filed application Serial No. 650,284,filed February 26, 1946, and now abandoned.

In the aforementioned cases I have disclosed an apparatus and method forburning various fuels such as oil, gas and pulverized solids such ascoal. A vortex or hollow column of air is established, as for example,by forcing the combustion air at a relatively high velocity betweentangentially disposed blades of an open ended annular -or cylindricaltuyre. The convergence of the respective air paths creates a rotationaleect which in turn, by centrifugal forces acting on the air, establishes`a substantially hollow vortical vair column. The fuel is introducedinto this vortical column and becomes intimately atomized or homogenizedas it follows a generally helical path through the tuyre and is thendischarged into the adjacent combustion chamber as a thin hollow ca lumnor stratum of fuel-air mixture.

Such a mixing or burning is especially important with various grades ofliquid fuel for as the liquid particles necessarily travel at a velocitysomewhat less than the air, there is a constant shearing action as theoil particles travel through the inflnite number of layers of air, eachrotating at a diierent velocity whichvaries with the distance from thecentral'axis. As the largest oil particles tend to be thrown outward tothe blades, they are further sheared by the viscous drag of incoming airwhich opposes the centrifugal effect. With such a procedure, fuelparticles as small as microns can` be readily made and the resultingfuel-air mixture which is discharged as a high velocity stratum orvortical column is adapted to high eilc'iency combustion in an adjacentcombustion chamber.

It is essential to most eiiicient combustion that the vortical characterof the air-fuel mixing be not prematurely dissipated as the mixturepasses into the larger combustion chamber. In accordance with myinvention, I provide for the maintenance of this intimate mixture by notonly continuing the high rotational eifect but increasing it. It will beappreciated that as the initial vortex that is established by anentering air velocity of from 50 to 150 ft. per sec. and as only a partof the tuyre end opening is utilized for the gaseous discharge while thecentral core is a low pressure inlet zone resulting from the partialvacuum formed. the net gaseous discharge may be at a velocity severaltimes as great` as that oi' the entering air.

It will also be appreciated that the greatly increased temperature inthe combustion zone will cause such a volumetric increase in theair-fuel mixture that the combustion zone must necessarily be greater inproportionate volume, to preserve the entering gas velocity. Actually Ipredetermine the combustion chamber dimensions and shape to provide aunique closed or compact flame pattern which is also of a vorticalcharacter. In appearance this flame appears annular and to surround ahollow core, which is likewise a zone of reduced pressure and the flamewhich is thus partially heated by convection and radiation. There isactually a recycling of the fuel into the flame front which not onlyprovides a reignition of any particles that may escape from the hottestpart of the flame, but also maintains an unexpected flame stabilizationand materially reduces the tendency of the unburned particles to formcoke on the combustion chamber wall.

A further important advantage of the vortical combustion pattern is ofcourse, the compactness of the ame. As the fuel-air mixture is directedsubstantially tangentially, and vthen limited by the annular characterof the combustion chamber, fuel is not thrown out of suspension and avery intense combustion is accomplished in a relatively short totallength of chamber. For many installations this is of highly criticalimportance, after-burning and flame impingement being generallyobjectionable and completely avoided herein. That the combustion issubstantially complete is indicated by CO2 analysis that show as high as15% CO2 in the products of combustion. l

The low pressure air (6" to 16" water gauge) through the-tuyre, thusperforms the multiple functions of breaking the fuel into discreteparticles of such size (20 microns) as are readily combustible. ofentraining the aforesaid particles and suspending them uniformlytherein, and :conveying the aforesaid particles in uniform suspension tothe burning zone wherein they are burned with substantially only the airtheoretically necessary for combustion. Secondary air may be added ifdesired but ordinarily it is not required in the usual commercial sense.A tuyre will cause the entrainment and atomization of nearly equalproportions of fuel and air on a pound-for-pound basis and the requiredamount of air for combustion may be passed through the relatively largeblade openings with a nominal pressure drop. In this way the fuel isgiven only sufficient head as to carry it to the vortical air column.

Preferably the combustion chamber for industrial installations isrefractory lined and thus becomes radiant and further maintains flamestability. It is possible however for special installations such as ingas turbines. aircraft, etc. where cost may be of less importance thanother factors, to use alloy metal name tubes. It is also customary inindustrial installations to make the combustion chamber cylindricalalthough other annular shapes may be employed and in at least one casein which low capacity is customary, I have shown a combustion chamberhaving a parabolic section which is truncated and closely fits over theend of the tuyre. Such a construction also has the advantage ofshielding the tuyre face and permits a gradual increase in the diameterof helical path of the fuel in the burning zone. It further avoids apossible disentrainment of the fuel from the entraining air.

My present invention is thus primarily laddressed to the operation andstructure of a combustion chamber into which a vortical or hollow columnof an intimate air-fuel mixture is discharged at a relatively highvelocity and in a helical path by any suitable fuel-air mixing device.It results in two name fronts in which the outer eddy or whirl providesprimary ignition with a reduced air supply while reignition andstability are accomplished with a normal air supply. At the same timethe inner eddy or whirl pulls in the flame, accomplishing a recycling ofthe fuel and creating intense combustion. It distinguishes from my priorapplications for patent which were primarily drawn to the use of thetuyre as the most effective means for establishing such a high velocityair-fuel mixture. I am aware that other apparatus, however, will to amore or less satisfactory degree, create an intimate air-fuel mixtureand its directional and velocity characteristics by which the eddies aredeveloped for the closed flame pattern.

The following description concerns a preferred form of embodiment of myinvention and is to be taken with the attached drawing illustrativethereof, and in which:

Fig. l is a substantially central vertical cross section of my burnerand adjacent combustion chamber.

Fig. 2 is a transverse cross-section taken substantially along the line2-2 of Fig. 1. J

Fig. 3 is a partial vertical cross section of a modified form ofcombustion chamber, and

Fig. 4 is a partial vertical cross sectional view through a stillfurther modified form of burner and combustion chamber.

As specifically shown in Fig. l, the combustion apparatus is adapted formounting in a furnace, boiler, or other heat absorbing unit having awall I which in this embodiment is afioor or 4 other horizontal wall.Within the heat absorbing unit is the combustion chamber II and theburner or fuel mixer assembly I2 is mounted adjacentv the closed end ofthe combustion chamber.

In this preferred construction and to better describe the operation ofthe combustion apparatus, the `burner or mixer I2 is shown as thecylindrical tuyre which is more specifically the subject of theaforesaid applications for patent. It has the closed end Il and the sidewall is formed by a plurality of generally tangential shallow vanes orblades I8 extending from the closed end Il to the open end of the tuyre.For economy, these blades may be stamped out of the tuyre wall but itwill be understood that they may be separate blades and that they mayoverlap or be streamlined as desired. They form a plurality of elongatedsubstantially rectangular inwardly converging air inlets or ports I1.

The tuyre l2 is generally .provided with a face plate I8 which extendsto a surrounding casing 20 serving as a windbox enclosing the air inletsor slots Il, and to which air may be introduced through inlet 22. Itwill be understood that this air, under a suitable pressure of from 6 to16" water gauge, and in sufiicientvolume to supply a velocity throughthe air paths between the blades of from 50 to 150 ft. per sec., will besupplied as by a suitable blower (not shown). 'I'he air entering thetuyre thus establishes such a rotary movement as to form a centralvortex or partial vacuum zone which results from the centrifugalconcentration (with a radial force in excess of times gravity) of theair along the wall as schematically represented by line X. This is aparabolic section having its theoretical vertex outside the tuyre sothat the column is substantially hollow or open throughout its length.There is thus no opportunity for a central outward discharge from thetuyre.

Fuel is introduced to this vortical column from the fuel reservoirindicated at 24 which may surround the closed endv Il of the tuyre I2.In this construction, the reservoir 2l has the nature of a. shallow panthe side of which extends at 24a to partially overlap the ends of theblades I6. As the fuel in the reservoir 24 is exposed to the air passingthrough the air paths between the blades I6, it will be entrained andcarried into the vortical air column therein. The fuel feed line to thereservoir 24 is indicated at 26.

By maintaining a velocity of air in the desired range, a continuousdischarge of the airfuel mixture from the open end and adjacent the wallof the tuyre is accomplished. It is found that the rotational effectactually produces a central vortex of reduced pressure in the tuyre withthe result that the discharge velocity of the air-fuel mixture is inexcess of the velocity of the air through the air paths I1. This causesa discharge of the air-fuel mixture as an annular stratum at an angularrelation to the wall of the combustion chamber II. No central baille isnecessary to maintain the hollow column eil'ect established by the highrotational effect of the entering air.

It is found on observation that the direction of this air-fuel mixtureis in the general direction of the line Y which is to say about 30 to 45to the longitudinal axis of chamber Il. As the mass is also rapidlyrotating however, and being under combustion conditions, there aregenerated the so called inner" eddies or whirls represented by line Zwhich is formed into the central low pressure core of the combustionchamber, as well as external or outer eddies or whirls represented bythe line .li These are formed as a result of the change of area of thecross section of the air-fuel column in moving from the tuyre to thelarger combustion zone. This is analogous to an orifice effect and isemphasized by the simultaneous rotation of the air-fuel mass in thecombustion zone about an axis normal to the closed end of the combustionzone.

This closed type of flame pattern depends on a combustion zone having arelative diameter and length with respect to the diameter of theintroduced stratum oi.' air-fuel mixture. I have found that in all casesutilizing all primary air as mixing air, that the inner diameter of thecombustion chamber (big end) must be at least 1% times and generally notmore than 4 times the tuyre or mixing device diameter. The mosteffective constructions have not exceeded 3 times the tuyre diameter itbeing understood that economy dictates as small a unit as possible. Inv

each case the length of the combustion chamber has been approximatelythe same as its diameter and this length varies from as low as a/m to asmuchas 1.5 times the diameter. Generally the best performance on liquidvfuels has been with diameter and length approximately equal. Thediameter is critical to prevent loss of vortical effect and the lengthmust be sufliciently great to assure a chamber within which the burningis substantially completed.

The refractory curb or combustion chamber tends to stabilize sustainedcombustion also because of the reradiation of the flame back from thecurb to the burning fuel particles or vapors and because the whirlingaction of the air-combustion gas mixture maintains these burning fuelparticles in suspension until combustion is complete. The whirling flameserves to reignite the mixture if there is a tendency for the burningllame to be quenched with the admission of greater amounts of air.

As a practical example of commercial units utilizing low pressure airand liquid fuels, the following table sets forth approximate dimensionsof units for various heat capacities.

Tuyere (70 F.'

Lgth.)

' Throat Diameter Million B. t. u.

Inches 1l 15 Starting up the burner is not a major problem asthe air isfirst started to establish the vortex and thereafter, the fuel beingturned on, the combustion is initiated by a torch or other means appliedto the center core or behind the outer eddy. With gas, ambienttemperatures are appropriate for both the air and gas but with heavierfuels, some preheating will be found to` aid combustion and avoidcoking. Using Bunker C fuel oil with air and oil preheat of about 250 F.is most satisfactory and asphalt may be burned when the air and asphaltare preheated to about 450 F.

With heavy duty industrial constructions, the cylindrical shape ofcombustion chamber is easi- ,withstanding combustion temperatures.

est to install and maintain and it provides both the internal as well asthe external eddies which do so much to stabilize the flame. It is notessential that this shape be strictly followed, although the combustionchamber must be annular to most effectively take advantage oftheintroduced vortical air-fuel column. In Fig. 3 for example I have showna paraboloidal type of combustion chamber for small furnaces withrelatively low heat input and with air pressures and velocities near theminimum that will successfully operate with this type of burner andcause a substantial vortex within the tuyre.

In this case, I have provided a curb or refractory chamber generallyshown at 30 which is adapted to closely embrace and be mounted upon thetop plate :ilv of a tuyre 32. This top plate extends to the wall of thecasing or shell 33 through which the air is directed and thence forcedthrough the tuyre openings to form the vortical column of air as in theprevious construction. The fuel, which is also introduced to this aircolumn, is thus discharged as an open column in a thoroughly mixedcondition into the burningzone formed by the refractory chamber.

The shape of the central opening in this chamber is considered to bemost important to prevent a premature discharge of the fuel from the airwhich may occur from a sudden change of velocity as the mixture movesout of the restricted tuyre area. For this reason I consider iteffective to form this opening as a surface generated by rotation of aparabola so that the increase in cross sectional area is comparativelyslow as coompared with the outward movement of the air-fuel column tothe llame combustion.

In this construction, the burning zone or combustion zone is spaced fromthe casing or shell 33 and the top plate 3| by the refractory 30 andthus relieves these parts of the necessity for By maintaining theangularity and velocity of discharge of the air-fuel column, theseparate particles of fuel are burned well within the combustionchamber. The internal eddy resulting from the central low pressure zonedue to the high centrifugal force normal to the central axis of thecombustion chamber materially aids this combustion.

It has been my experience that the best way to produce a vortical columnof air and fuel is by forcing the air between the blades and introducingthe fuel into the resulting column. I have also introduced the fuel tothe air column as it discharges into the combustion chamber as shown inFig. 4. In this case the primary air passes through the tuyre 40 whichis surrounded by windbox 42 which in turn is mounted in the furnace wall44. The tuyre 40 is provided with a face plate 45 which extends to thesurrounding casing 42. The` face plate may be perforated whereby aportion of the air in the enclosure passes through the face plate tokeep the tuyre cool. A shield 45a may also be used above the face plate45 to aid in this purpose as more fully described in my copendingapplication, Serial No. 98,976, filed June 14, 1949. The

fuel may be introduced to this column as by conduit 46 having adistributing head or pressure atomizing spray nozzle 41 and to a certaindegree, the advantages of the vortical fuel mixing will be obtained.

It has the advantage that fouling of the blades iby fuel which may beotheerwise thrown out is completely avoided. It also has the advantage 7that the atomizing type of a simple nozzle or gun may be easilywithdrawn and replaced if it becomes fouled or for other reasonswithdrawal is necessary. It also permits the use of cold air for burningas the air is discharged into the combustion chamber 48 before the fuelis introduced to it.

The central nozzle type of fuel feed has, however, some disadvantages ascompared to the tuyre mixer of Figs. 1 and 3. It requires some pressureon the fuel to cause the desired atomization and distribution. It doesnot provide quite the intimacy of mix of air and fuel which isaccomplished by the long helical path and centrifugal forces applied bythe tuyre. It also has an exposed tip which tends to become radiantlyheated and will more rapidly cause coking. It is thus a somewhat lesseffective manner of feeding the fuel to the vortical column.

With this type of feed, and assuming a continued discharge of thevortical air column, there can still be a closed flame pattern withinthe combustion chamber if it has the critical dimensions characteristicof the chamber in Fig. 1. The chamber should not be less in diameterthan about 11/2 times the diameter of the tuyre opening and it should benot greater than 4 times, and preferably times the diameter of the tuyreopening. In length, the combustion chamber should be nearly as long asits diameter.

In the disclosed embodiments of my invention the axial length of theside wall of the combustion chambers is from 0.8 to 1.5 times the insidediameter of the side wall at the open front end, and the circularopening in the closed rear end of said chambers is from 0.25 to 0.67times the diameter of said open front end.

I claim:

l. The combination comprising a combustion chamber having a rear walland a closed side wall and open at the front end, the side wall having.the shape of a surface of revolution, the axial length of said sidewall being from 0.8 to 1.5

times the inside diameter of the side wall near the front end of thechamber, and said rear wall having a circular opening therein which hasa diameter of from 0.25 to 0.67 times the diameter of the chamberadjacent its rear end, and means for introducing air forwardly throughsaid opening in the form of a rotating annulus spaced from the side wallof the chamber, whereby a iiame produced in said combustion chamber willform whirls of iiame gases within the annulus for rapidly heating therotating annulus issuing from said opening and thereby stabilizing thename against extinguishment at high rates of flow, said means includinga mixing chamber open at its front end and closed at its rear end andhaving an annular side wall formed with a plurality of circumferentiallyspaced tangential air inlet slots extending to the rear end and a casingenclosing the air inlet slots of the mixing chamber, means to pass airinto the casing to establish a vortex in the mixing chamber which passesas an annulus to the combustion chamber, and means for supplying fuel tothe rotating air annulus.

v2. The combination as claimed in claim 1, in l 8 length of said sidewall being approximately the same as the inside diameter of the chamber,and said rear wall having a circular opening therein which has adiameter of 0.33 times to 0.67 times the diameter of the chamber, andmeans for introducing an inflammable mixture forwardly through said rearwall opening in the form of an annulus spaced from the side wall of thechamber whereby a flame formed by'igniting said inflammable mixture willform whirls of flame gases both within the annulus and between theoutside of the annulus and the chamber side wall for rapidly heating themixture issuing from said rear wall opening and thereby stabilizing itagainst extinguishment at high rates of flow, said open at its front endand closed at its rear end and having an annular side wall formed with aplurality of circumferentially spaced tangential air niiet slotsextending to the closed rear end and a casing enclosing the air inletslots of the mixing chamber, means to pass air into the casing toestablish a vortex in the mixing chamber which passes as an annulus tothe combustion chamber, and means for supplying fuel to the rotating airannulus.

4. A method of burning fluid fuel utilizing a mixing chamber wherein thefuel and air are mixed, and an adjacent coaxial combustion chamber witha lateral wall having the shape of a Asurface of revolution in which theair-fuel mixture is burned, which lcomprises passing the air through themixing chamber at such a rate and angular relation to the axis of thelmixing chamber that there is formed an outwardly moving rapidlyrotating annular mass of airI having a centrifugal force component inexcess of one hundred times gravity, intermixing fluid fuel with therotating mass in the mixing chamber, discharging the air-fuel mixture asan annular vortical mass axially 'into the combustion chamber,initiating combustion in and burning said air-fuel mixture in saidcombustion chamber, and constraining the combustion to a spiral pathhaving a diameter at least as great as the discharged annular mass andnot exceeding three times the diameter of said discharged annular massof fuel-air mixture, and a length substantially as great as its diameterwhereby the vortical effect of said fuel-air mixture is substantiallypreserved in the combustion chamber for sufficient time to induceproducts of combustion into the central portion of the combustionchamberso that flame stabilization is accomplished.

5. A method of burning fluid fuel utilizing a mixing chamber wherein thefuel and air are mixed, and an adjacent coaxial combustion chamber witha lateral wall having the shape of a surface of revolution in which theair-fuel mixture is burned, which comprises passing the air through themixing chamber at such a rate and angular relation to the axis of themixing chamber that there is formed an outwardly moving rapidly rotatingannular mass of air having a centrifugal force component in excess ofone hundred times gravity, intermixing'iluid fuel with the rotating massin the mixing chamber, discharging the airfuel mixture as an annularvortical mass axially into a sharply enlarged combustion chamber,initiating combustion in and burning said air-fuel mixture in saidcombustion chamber, and constraining the combustion to a spiral pathhaving a diameter greater than that of the discharged annular mass andnot exceeding three times the diameter of said discharged annular massof assenze air-fuel mixture, and a length substantially as great as itsdiameter whereby the vortical effect of said air-fuel mixture issubstantially preserved in the combustion chamber for suiiicient time toinduce whirls of flame gases into the central portion of the combustionchamber and whirls of flame gases between the outside of said spiralpath and the sidewall of the combustion chamber adjacent its inlet endso that flame stabilization is accomplished. fl

6. A method of preparing and burning liquid fuel utilizing a tuyre openat its outer end and closed at its inner end, and having an annular sidewall formed with a plurality of circumferem tially spaced tangential airinlet slots extending to the closed inner end, and a casing enclosingthe air inlet slots of the tuyre, said method comprising feeding air tosaid casing throughout the length and periphery of the slotted side wallof the tuyre and through the slots tangentially into the tuyre, said airbeing fed at such rate and angular relation to the axis vof the tuyrethat there is formed a forwardly moving rotating column of air with avacuum in the center thereof and having a forward velocity atleastseveral times the velocity of the inlet air to the casing, dischargingthe air as an annular vortical column into an elongated combustion zoneof restricted circular cross section spaced outwardly from said tuyre,intimately mixing liquid fuel in said vortical column by entrainmenttherewith to form a combustible fuel-air mixture, constraining thefluel-air mixture to a rotating forwardly moving annular vorticalcolumn, and initiating combustion in and burning said fuel-air mixturein said combustion zone as a rotating mass, said burning and theresulting gas' movement forming whirls of flamegases in the combustionzone for stabilizing the name against extinction and completingcombustion in a relatively short lineal distance.

7. A method of preparing and burning liquid fuel utilizing a tuyre openat its outer end and closed at its inner end, and having an annular sidewall formed with a plurality of circumferentially spaced tangential airinlet slots ex, tending to the closed inner end, and a casing enclosingthe air inlet slots of the tuyre, said method comprising feeding air tosaid casing throughout the length and periphery of the slotted side wallof the tuyre and vthrough the slots tangentially into the tuyre, saidair being fed at such rate and angular relation to the axis" of thetuyre that there is .formed a forwardly moving rotating column of airwith a vacuum in the center thereof and having a forward velocity atleast several times the velocity of the inlet air to the casing, rapidlyexpanding the outwardly .moving rotating column of air with a vacuum inthe center'thereof as `formed in 00- the tuyre by discharging saidcolumn of air as an annular vortical column into a sharply enlargedcylindrical combustion zone spaced outwardly from said tuyre and havingan entrance diameter which is between 11/2 and 3 times 65 the diameterof the tuyre and a length approximately equal to its diameter,intimately mixing liquid fuel in said vortical air column by entrainmenttherewith to form a combustible fuelair mixture, constraining thefuel-air mixture 70 to a rotating forwardly moving annular vorticalcolumn, and initiating combustion in and burning said fueleair mixturein said combustion zone as a rotating mass, said burning and theresulting gas movement forming whirls of name i gases within the burningrotating mass in the combustion zone and whirls of flames between theside walls of the combustion chamber adiacent its inlet end and saidburning rotating mass for stabilizing the iiame against extinction andcompleting combustion in a relatively short lineal distance.

8. The combination comprising a combustion .chamber having a rear Walland an annular side wall and open at the front end, the side wall havingthe shape` of a surface of revolution, the axial length of said sidewall being from ,0.8 to 1.5 times the inside diameter of the side wallnear the rear end of the combustion chamber, and said rear wall having acircular opening therein which has a diameter of from 0.25 to 0.67 timesthe diameter of the vchamber adjacent its rear end, and means forintroducing air forwardly through said opening in the form of a rotatingannulus spaced from the side wall of the chamber, said means including acylindrical tuyre open at the front end and closed at the rear end andhaving tangential ports therein, a casing enclosing the tangential portsof the cylindrical tuyre, and means for supplying fuel to the rotatingannulus, whereby a flame formed by igniting the inflammable mixture ofair and fuel will form whirls of name gases within the annulus forrapidly heating said mixturev adjacent said opening and stabilizing theilame against extinction.

9. The combination comprising a cylindrical combustion chamber having arear wall and a closed side wall and open at the front end, the axiallength of said side wall being from 0.8 to 1.5 times the inside diameterof the combustion chamber, and said rear wall having a circular openingtherein which has a diameter of from 0.25 to 0.67 times the diameter ofthe chamber, and means for introducing air forwardly through saidopening in the form of a rotating annulus spaced from the side wall ofthe chambe'r, said means including a cylindrical tuyre open at the frontend and closed at the rear end and formed with a plurality ofcircumferentially spaced tangential air inlet slots in the side `wallthereof, a casing enclosing the air inlet slots of the cylindricaltuyre, and means for discharging fuel under pressure into the rotatingannu1us,whereby a name formed by igniting the inammable mixture of airand fuel will form whirls of flame gases within the annulus for rapidlyheating said mixture adjacent said opening, and outer whirls adjacentthe side wall at the rear end of the combustion chamber for stabilizingthe flame against extinction.

r; ln: J. BLOOD/IER.

REFERENCES CITED The following references are of record in 'the nie ofthis patent: y

UNITED STATES PATENTS Great Britain ....g June 1i, 193i

